. Lyme arthritis presents a unique circumstance of a T lymphocyte infiltrative disease for which the causative agent, the spirochete Borrelia burgdorferi has been identified. In this capacity, Lyme arthritis is the cause of T cell receptor (TCR) repertoire skewing in synovium, as it relates to the inciting agent. This study will correlate a response to B. burgdorferi stimulation with two T cell biases that have observed in Lyme synovial T cells: (1) a skewing toward Vbeta7 and Vbeta13.1 expression; (2) a pronounced expansion of gamma-delta T cells. Specific aim 1 will examine whether the TCR-Vbeta and gamma-delta biases are due to an expansion of Borrelia-reactive T cells. Borrelia-stimulated Lyme synovial T cells will be examined by quantitative PCR of TCR-Vbeta expression, and cell cycle analysis using bromodeoxyuridine (BrdU) and propidium iodide (PI) combined with anti-Vbeta antibody staining and flow cytometry. Borrelia- reactive synovial T cell clones will be derived to examine their Vbeta repertoire and to use for Borrelia protein and peptide reactivity. Specific aim 2 will examine the possibility that the Vbeta repertoire bias results from selective elimination of T cells expressing certain Vbeta. This might result from superantigen-mediated apoptosis and will be explored using terminal deoxytransferase (Tdt) analysis of nicked DNA.An alternative is that the expanding gamma-delta cells are selectively cytolytic toward CD4+ cells, which diminish during Borrelia stimulation. Specific aim 3 examines the gamma-delta repertoire of Lyme synovial cells by PCR and sequencing to determine the degree of oligoclonality, particularly toward Vdelta. B. burgdorferi specific gamma-delta T cell clones will be derived to assess their specificity and further explore their potential cytotoxicity as a means of immune regulation in Lyme synovium.Collectively the studies will address important issues of TCR-Vbeta and TCR gamma-delta bias in Lyme synovium, determine the specificity of these T cells, and explore the potential immune regulatory pathways of Lyme synovial gamma-delta cells.The findings will suggest new strategies for therapeutic interventions at the level of specific T cell anergy, regulating gamma-delta cells, and possible vaccines based on immunodominant epitopes.